Project 8 is a next generation experiment aiming to directly measure the neutrino mass using the tritium endpoint method with a targeted sensitivity of 40 meV. Having established a new measuring technique, Cyclotron Radiation Emission Spectroscopy (CRES), the next development phase will demonstrate CRES on a large source volume, culminating in a pilot-scale CRES experiment with atomic tritium. A promising option is a mode-filtered, cylindrical, resonant cavity in which cyclotron radiation from magnetically trapped beta electrons only couples to the lowest eigenmode, maximizing effective volume and minimizing signal complexity. Recent progress in the experiment design, including a small scale cavity CRES proof-of-concept apparatus to demonstrate CRES in cavities and its scalability to large volumes are described.